1. Field of the Invention
The present invention relates an image pickup apparatus disposed at a distal end portion of an insertion portion of an endoscope, and specifically relates to an image pickup apparatus for an endoscope, the image pickup apparatus including an actuator apparatus for an endoscope, the actuator apparatus advancing and retracting a moving lens frame.
2. Description of the Related Art
Electronic endoscopes are used for observations or treatments, etc., of insides of living bodies or inspections or repairs, etc., of insides of industrial plant facilities. In endoscopic observations, it is demanded that optical characteristics, such as a focal depth, a formed image magnification and a view angle, for an observation target portion can be changed according to, e.g., a site to be observed or a purpose of the observation.
In recent years, image pickup apparatuses have been known which include an objective lens group in which one or more optical lenses included in the objective lens group can be moved in an optical axis direction, enabling adjustment or change of optical characteristics. For example, with an endoscope enabling normal observation and enlarged observation, a moving lens frame that can be moved in an optical axis direction, which is arranged in an objective lens group included in an image pickup apparatus, is moved to the distal end side or the proximal end side by means of a moving mechanism, providing a desired observation state.
The endoscopes are configured so as to, for example, enter a normal observation state when the moving lens frame is moved to the distal end side of the insertion portion of the respective endoscope and enter an enlarged observation state as the moving lens frame is moved to the proximal end side. Such endoscopes are in a maximally-enlarged observation state when the moving lens frame has been moved to the furthest on the proximal end side. It should be noted that an amount of movement of a moving lens arranged in an image pickup apparatus of an endoscope is set as a minute amount, for example, a range of 0.3 to 1.0 mm.
Meanwhile, for moving mechanisms that move a moving lens frame in an image pickup apparatus, e.g., mechanisms that advance and retract a wire connected to a moving lens frame via an operation lever or a drive motor provided in an operation section, or mechanisms including an urging spring and a shape memory alloy provided in an insertion portion of an endoscope to advance and retract a moving lens frame by means of energization and stopping energization are known.
For example, Japanese Patent Application Laid-Open Publication No. 2007-229155 discloses an endoscope that enables reduction in size of an image pickup unit including an actuator to achieve reduction in diameter of a distal end portion of an insertion portion of the endoscope. The endoscope includes an actuator unit that advances and retracts a moving lens frame in a shooting optical axis direction. The actuator unit includes, e.g., an urging spring and a shape memory alloy (hereinafter referred to as “SMA”) wire.
With such actuator unit, the moving lens frame in the image pickup apparatus is moved forward by an urging force of the urging spring in a non-energized state in which the SMA wire is extended, and is moved to the proximal end side by making the SMA wire enter an energized state to make the SMA wire contract against the urging force of the urging spring.